C++ Vector Initialization Methods | Programming Tutorials

Introduction

In this lab, we will learn about the different ways to initialize a vector in C++. We will cover the following methods:

Skills Graph

%%%%{init: {'theme':'neutral'}}%%%% flowchart RL cpp(("C++")) -.-> cpp/ControlFlowGroup(["Control Flow"]) cpp(("C++")) -.-> cpp/IOandFileHandlingGroup(["I/O and File Handling"]) cpp(("C++")) -.-> cpp/StandardLibraryGroup(["Standard Library"]) cpp/ControlFlowGroup -.-> cpp/for_loop("For Loop") cpp/IOandFileHandlingGroup -.-> cpp/output("Output") cpp/StandardLibraryGroup -.-> cpp/standard_containers("Standard Containers") subgraph Lab Skills cpp/for_loop -.-> lab-96167{{"Initializing a Vector in STL Using C++"}} cpp/output -.-> lab-96167{{"Initializing a Vector in STL Using C++"}} cpp/standard_containers -.-> lab-96167{{"Initializing a Vector in STL Using C++"}} end

Using push_back() method

The push_back() method is used to insert elements into the vector dynamically one at a time. This method increases the size of the vector by one and inserts the new element at the end of the vector.

#include<iostream>
#include<bits/stdc++.h>

using namespace std;

int main()
{
    cout << "Using push_back() method\n\n";

    //create an empty vector
    vector<int> v;

    //insert elements into the vector using push_back()
    v.push_back(1);
    v.push_back(2);
    v.push_back(3);

    //prining the vector
    cout << "The elements of the vector are: ";

    for (int i : v)
    {
        cout << i << " ";
    }

    cout << "\n\n\n";

    return 0;
}

To compile and run the above code, open the terminal and navigate to the file location ~/project. Type the following command to compile and run the program:

g++ main.cpp -o main && ./main

Initializing all the elements with a specific value

We can initialize all the elements in the vector with a specific value using the following constructor:

vector<int> v1(n, value);

Here, n represents the number of elements we want to initialize and value represents the value to which all the elements are to be initialized.

#include<iostream>
#include<bits/stdc++.h>

using namespace std;

int main()
{
    cout << "Initializing all the elements with a specific value\n\n";

    //creating a vector of size 5 with all values initalized to 10
    vector<int> v1(5, 10);

    //printing the vector
    cout << "The elements of the vector are: ";

    for (int i : v1)
    {
        cout << i << " ";
    }

    cout << "\n\n\n";

    return 0;
}

To compile and run the above code, open the terminal and navigate to the file location ~/project. Type the following command to compile and run the program:

g++ main.cpp -o main && ./main

Summary

In this lab, we have learned about the different ways to initialize a vector in C++ using push_back() method and constructor. We have learned how vectors are beneficial over arrays due to their dynamic size and ability to resize automatically. We have also demonstrated C++ code to understand and implement the above methods. You can now write your own code using these methods to initialize vectors in C++.